Protection Island, Washington, is located at the southeast end of the Strait of Juan de Fuca in the rain shadow of the Olympic Mountains (approximate rainfall=41 cm/year). The 160-hectare island contains one of the largest breeding colonies of seabirds and harbor seals (Phoca vitulina) in the Pacific Northwest. In 1988 most of the island was designated as the Protection Island National Wildlife Refuge. While Protection Islandís habitat structure has changed little since George Vancouver's 1792 description of the island, published information on its flora consists only of incidental remarks appended to faunal studies. As part of a long-term assessment of Protection Islandís biodiversity, vascular plants were collected from 1997-2000. During June-August 1999, plant diversity and density were sampled in 311 randomly-selected, 1 x 1-m quadrats along 15 transects. Introduced species accounted for 42% of the 106 species collected overall, and for 55% of 20 species of grasses. Exotics accounted for most of the grassland cover. Field bindweed (Convolvulus arvensis) and Canada thistle (Cirsium arvense) were particularly invasive. Snowberry (Symphoricarpos albus) was common along north-facing slopes. Two small forested areas, dominated by Douglas fir (Pseudotsuga menziesii), were commonly bordered by Douglas maple (Acer glabrum), Pacific madrone (Arbutus menziesii), ocean spray (Holodiscus discolor), and Nootka rose (Rosa nutkana). Weedy species dominated the sparsely-vegetated nesting areas of rhinoceros auklets (Cerorhinca monocerata) and glaucous-winged gulls (Larus glaucescens). A vegetation map of the island was created using ground-truthed, aerial photographs. A species-association matrix highlights correlations among species distribution patterns. Results from this study have raised questions about the impact of previous agricultural practices, real estate development, and fire prevention on the islandís grassland community. They have also led to hypotheses about plant/nesting-bird interactions and about the value of controlled burns of the islandís grassland areas. These hypotheses are currently being tested.

Key words: diversity, flora, grassland, Protection Island WA, tall-grass prairie